A conventional solar collector comprises an enclosure made from a transparent single- or multi-layered polymer material having a width L and consisting of a central cylindrical portion having radius R, two lateral cylindrical portions that have radius r and are connected to the edges of the central cylindrical portion, and a plane portion tangential to the lateral cylindrical portions, two end-face covers installed on the enclosure end faces, and a heat-receiving device arranged inside the enclosure for transferring heat to a heat carrier, the front side of the heat-receiving device being coated with a selective coating while the rear side thereof having thermal insulation. A heat-receiving device has width H and thickness t. The enclosure width H and values of radiuses R and r satisfy the following conditions:5H>R>3H; 1.5t>r>(√{square root over (2)}/2)t; 1.1H>L>1.05H. 
The heat-receiving device can be produced in the form of a flat absorber with channels for circulation of a liquid heat carrier or in the form of a storage tank (see RU 2224188 C1).
However, in the conventional solar collector with a flat and bent heat receiver (absorber), the shape of the enclosure is not optimized with regard to maximal efficiency in combination with low cost and a minimal material/power ratio. In the conventional solar collector, the configuration of the transparent enclosure is linked to a thickness of the flat absorber according to the following ratio:1.5t>r>(√{square root over (2)}/2)t. 
Such a relationship between the dimensions of t and r is optimal for an absorber beveled on the sides. In this case, thickness t of the absorber is defined as the distance from the edge of the bevel to the plane of the absorber. In widely used absorbers that do not have side bevels, the aforementioned relationship between r and t loses its meaning since the bevels are absent, and criteria other than those mentioned above are needed for optimizing the enclosure shape. Furthermore, no provisions are made in the conventional solar collector for use of absorbers having a curvilinear shape.
A method known in the art for manufacturing a solar-collector enclosure involves cutting out four triangular slots in the surface of the sheet and arranging the slots along both edges of the sheet and at predetermined angles to the sheet edges. Distances between the slots correspond to the dimensions of the collector sides. Shelves with triangular slots are bent from both edges of the sheet, the sheet is bent around the sides of the collector along the lines that connect apexes in the respective triangular slots, and the free edges of the sheet are then interconnected (see WO 00/03185 A1).
However, the above-described conventional method for manufacturing a solar collector enclosure requires that the triangular slots that are cut out from the sheet be strictly aligned on both sides of the sheet. If this is not done, the angle of the fold will be skewed. Therefore, this operation requires the use of precision equipment. Because the sheet has a certain thickness, it is impossible to achieve a direct angle at the corner of the fold, and the angle that is formed leads to a permanent slit on the face side where the edges of the triangular slots must merge at 45°.